Oilfield drilling, stimulation, and production activities often cause microearthquakes (microseismic events), either by compacting rock, propagating fractures, or relieving shear stress. Such events may result from reservoir stimulation, hydraulic fluid injection, and reservoir depletion, just to name a few examples. Microseismic events cause pressure and/or shear waves to propagate outward in all directions from the event. Receivers up to a kilometer away have been used to detect and locate such events in rock types ranging from unconsolidated sands, to chalks, to crystalline rocks. It is expected that the frequency, intensity, and spatial distribution of microseismic events will reveal valuable information about the chemical, hydraulic, and/or mechanical processes occurring in the volume around boreholes in the earth. For example, microseismic monitoring is often used to map new fractures as they are created by hydraulic fracturing or water flooding techniques.
Microseismic monitoring is usually performed from one or more monitoring wells each having an array of wireline receivers. With the receivers deployed in several wells, the microseismic event locations can be triangulated as is done in earthquake detection, i.e., by determining the arrival times of the various p- and s-waves, and using formation velocities to find the best-fit location of the microseismic events. However, multiple monitoring wells are not usually available. With only a single monitoring well, multiple wireline directional receiver arrays may be used to locate the microseismic events. Once the microseisms are located, the actual fracture is usually interpreted within the envelope of microseisms mapped, but very accurate detection and location is usually necessary to determine the precise length, direction, and height of the created fractures. Existing systems and methods may be unable to provide sufficient accuracy without substantial cost and/or computational complexity.